Screens with rotating shafts are well known in the prior art. One example of a separator of this type is that disclosed in U.S. Pat. No. 4,037,723, issued July 26, 1977. The apparatus of this patent incorporates interleaved rotating disks rotating in the same direction whereby material fed onto the tops of the disks will be passed along from one row to the next, the finer material dropping through the spaces between adjacent disks. The coarser material is carried along on top of the disks whereby separation of fine and coarse material may be obtained. The separator of U.S. Pat. No. 4,037,723 provides means for accurately spacing the disks of one row relative to the those of an adjacent row and for changing the spacing of the disks. This can only be accomplished during separator downtime. The distance between the shafts employed in the separator is fixed.
U.S. Pat. No. 4,301,930, issued Nov. 24, 1981 also shows a screen apparatus of the type having a series of rotating shafts, each of which has a longitudinal series of concentric screen disks which mesh with the screen disks of adjacent shafts. The screen disks are carried by tubular modules mounted in end-to-end relation on the shaft. The shafts utilized in the machine remain a fixed distance from one another.
U.S. Pat. No. 4,658,964, issued Apr. 21, 1987, relates to a screen composed of a bed of rotary disks in spaced relation and formed in the periphery with undulating surfaces for constantly agitating the waste material to be screened. The apparatus includes a controllable drive system for the rotary disks which adjusts the speed of the disks. The shafts upon which the disks are mounted remain in fixed position relative to one another.
U.S. Pat. No. 4,266,676, issued May 12, 1981, also relates to apparatus for separating material. The separator disclosed in this patent incorporates a series of non-circular disks, such as elliptical or three lobed disks. These disks are mounted on each shaft and interspaced with the disks on adjacent shafts. There is no disclosure in U.S. Pat. No. 4,266,676 of varying the distances between the shafts themselves.